In a wide variety of industrial processes the primary product or by-product is at one time or another present as solid material wet with a liquid. This solid material must be produced as a "dried product." The drying operation is normally carried out in a so-called dryer.
There are two primary types of dryers. In one primary type, heat surfaces heated by steam under pressure are provided and the wet solid material being dried does not come into direct contact with the steam. In the other primary type, hot gasses are brought into direct contact with the wet solid material. In each case, the heat added must equal the sensible heat of the mass plus the latent heat of vaporization of the liquid present in the wet solid material. The liquid after being vaporized is usually swept away with air or an inert gas in dryers that utilize heated surfaces or by the hot gasses themselves in dryers which function by direct contact drying.
While the primary types of dryers mentioned are satisfactory and have achieved wide commercial acceptance, they are generally somewhat undesirable from the viewpoint of efficiency with respect to heat utilization. For example, in known heated surface evaporators and dryers employing direct contact with hot gasses, the vaporized liquid from the wet solid material is generally simply removed, collected and optionally condensed without any utilization of the latent heat energy possessed thereby. Consequently, such known systems are disadvantageous in this respect, as well as requiring large amounts of heat energy to provide a substantially dry product, and there exists a need for providing a drying process for a wet solid material and an apparatus for achieving the same which do not exhibit the above mentioned short-comings. The present invention fulfills this need.